1. Field of Invention
The present invention relates to devices for locating the source of sound waves or acoustic emission and in particular for determining the location of a sound source of sound waves or acoustic emission emitted from a structure.
2. Prior Art
Locating the source of sound, etc. can be accomplished from the difference in time which a sound wave takes to reach a plurality of sensors. One of such conventional devices is described in the following example and in such example the determination of the acoustic emission (hereinafter abreviated as AE) such as elastic waves generated when a solid body is deformed or breaks is made so that the breaking of the body can be predicted and data can be used for research in the science of materials.
In FIG. 1 is shown a folded out view of a large tank with sensors 2 distributed on side wall 1 of the tank. The symbols attached to each sensor indicates the address of the sensor. There are eight sensors in the direction of the x-axis and five sensors in the direction of the y-axis or all together forty sensors distributed in the form of a matrix. In FIG. 2 is shown a block diagram of a conventional device which includes a processing circuit 3 containing an amplifier and a shape forming circuit. A detected signal from the sensor 2 is applied to the signal processing circuit 3 and converted into a pulse signal having a peak magnitude as well as a detection time. The conventional device further includes a computation circuit 4 which identifies the order in which each sensor has received the AE signal on the basis of the phase difference of the input signal. At the same time, the computation circuit combines the first and second signals in order of detection as well as the first and third signal in order of detection and sends these as an output to time difference measurement circuits 5-1 and 5-2 wherein the detection time difference of each sensor 2 is measured.
Shown in FIG. 3 is a diagram for explaining the method of locating the AE source from the data. The determination is made as the crossing point of two hyperbolas, one of which is the trajectory A of the point at which the time difference is constant between the signal receiving sensor at the first position 2-42 and the signal receiving sensor at the second position 2-41 and the other of which is the trajectory B of the point at wich the time difference is constant between the signal receiving sensor at the first position 2-42 and the signal receiving sensor at the third position 2-32.
In a conventional device constructed as described above each sensor 2 is always in contact with a signal processing circuit 3. Since the AE is a weak sound wave, the sensor's possible range of detection is only on the order of 1 to 2 meters even in the case of steel materials. If the object is a large structure, it is necessary to distribute a large number of sensors and it becomes necessary accordingly to have a position locating device equipped with a multi-channel signal processing circuit. When the object of measurement is a water reservoir dam, for example, the necessary number of sensors may be a large as tens of thousands. Thus, the real world utilization of the conventional devices is extremely difficult and expensive.